Thermal growth compensation and mounting for plastic dishwasher tub

ABSTRACT

The lower sidewalls of a unipartite, plastic dishwasher tub are formed with integral ledges or horizontal walls which perform a dual load support function, viz. that of supporting the tub on a base assembly and providing a lower dishwasher rack support track. Compensation for thermal growth of the tub walls inwardly of the wash chamber is achieved by incorporating a deliberate, outward bow into the tub walls. This is accomplished, in the case of the lower, top and back walls by molding the same with an unstressed outward bow while the unstressed, planar sidewalls are deformed mechanically.

UnIted States Patent 1191 1111 3,834,783

Jenkins Sept. 10, 1974 54] THERMAL GROWTH COMPENSATION 3,679,282 7/19721411111111311 3121311 AND MOUNTING FOR PLASTIC FOREIGN PATENTS ORAPPLICATIONS DISHWASHER TUB 1,006,627 0/1947 France 312/214 Inventor:

Assignee:

Thomas E. Jenkins, Louisville, Ky.

General Electric Company, Louisville, Ky.

Filed: Dec. 29, 1972 Appl. No.: 319,555

US. Cl 312/253, 312/311, 312/350 Int. Cl A47b 96/00 Field of Search126/19 R; 312/100, 330,

References Cited UNITED STATES PATENTS 7/1962 Abresch et al 312/3486/1965 Dutcher et al.. 312/228 10/1967 Krzewina 312/348 X 5/1968 Dicken,Jr. 312/311 12/1969 Kaufman et al. 312/311 X Primary ExaminerPaul R.Gilliam Assistant ExaminerWilliam E. Lyddane Attorney, Agent, orFirmFrancis H. Boos 5 7] ABSTRACT The lower sidewalls of a unipartite,plastic dishwasher tub are formed with integral ledges or horizontalwalls which perform a dual load support function, viz. that ofsupporting the tub on a base assembly and providing a lower dishwasherrack support track.

Compensation for thermal growth of the tub walls inwardly of the washchamber is achieved by incorporating a deliberate, outward bow into thetub walls. This is accomplished, in the case of the lower, top and backwalls by molding the same with an unstressed outward bow while theunstressed, planar sidewalls are deformed mechanically.

6 Claims, 4 Drawing Figures THERMAL GROWTH COMPENSATION AND MOUNTING FORPLASTIC DISHWASHER TUB BACKGROUND OF THE INVENTION The invention isdirected to large capacity front loading dishwashers of the typenormally comprising a permanent installation and employing upper andlower dish supporting racks as opposed to the smaller, low capacity,portable and/or top loading dishwashers. The reason for the distinctionis that the ultimate objective of the invention is the employment of aunipartite plastic tub in large capacity, front loading dishwashers andwhile some of the problems presented by a proposed use of such a tubwould be common to dishwashers of either type; the majority aredistinct. Typical distinctions relate to increasing wall flexibilitywith increasing area, the absence of encompassing metal housings,greater tub shape complexity and additional interior tub mountings suchas dual rack support structures. Accordingly, the ensuing backgrounddiscussion relates primarily to front loading dishwashers of the typenormally adapted for a permanent, under cabinet, installation.

The high temperature, corrosive environment to which automaticdishwasher chambers are subjected dictates that the surfaces of thoseinternal components in contact with such environment be either highlyresistant, or immune, to corrosion. Corrosion resistant metals such asstainless steel represent a substantial cost factor in this highlycompetitive appliance field and the long term industry trend has beentoward the use of inert materials to resist the corrosive effects of thechamber environment which are magnified adjacent the usual metal tubseam welds. Insofar as the tub itself, representing the far greaterinternal surface area exposure, is concerned; the general trend in theUnited States has been toward the application of an adherent plasticcoating to the tub interior while European manufacturers have gone moreto the use of plastic tub lin ers. In either event, the basic structuraland design pa rameters that have prevailed since the advent of themodern front loading automatic dishwasher remained valid. This for thereason that overall dishwasher design parameters, both as regardsutility and structural integrity, are virtually unaffected by whetherthe conventional metal tub is coated, lined or exposed.

Conceptually, the use of a unipartite plastic dishwasher tub, i.e., onenot requiring a more rigid backing or outer support structure,represents a substantial advance in the art. Exemplary are the greatlydecreased cost factors of a molded plastic tub vis-a-vis that of a metaltub requiring a further coating or lining operation; reduction infinishing labor requirements and particularly tub welding operations;longer tub life due to corrosion resistance which is independent offaulty coating procedures or chipping; decreased thermal and acousticaltransmission thus minimizing the need for separate insulation; and alesser inventory requirement for separable components susceptible ofintegral molding with the tub.

The reduction to practice of such a concept, as applied to front loadingdishwashers on an assembly line basis, however, present a myriad ofproblems which arise as a requirement for different approaches to thoseengineering considerations which had previously been predicated upon theuse of a metal tub. The distinctions are primarily those associated withmaterial strength, the unusually high temperature environment to whichthe tub is subjected and considerations relating to plastic moldingprocedures. Thus, while the structural integrity of a metallic box beamshape defined by the conventional front loading tub is more thansufficient to resist excessive wall deformation as a function of normalloading forces as during installation, adjustment or use and temperaturevariations from room ambient to approximately 255 F.; such normallyapplied loading forces would, in the absence of appropriate compensatingstructure, produce unacceptable wall defor-. mation in a like configuredplastic tub. The use of strand-like reinforcing fillers such. as fiberglass would, seemingly, ameliorate the overall problem of walldeformation. In actuality. however, the presence of such reinforcingfibers not only effect tub discoloration as discussed below, but theirrandom distribution precludes an accurate prediction of thermal growthcharacteristics which is an essential parameter in the design of thenecessary compensating structure herein dis cussed. Similarly, impactstrength is normally of little moment in the design and installation ofmetallic tubs but is a matter of major concern in plastic tub design.Furthermore, various structural features appearing in a formed plastictub as an incident of the forming operation create problems notpreviously associated with metal tub fabrication. Exemplary of thelatter distinction are the presence, on the finished product, of moldlines and/or mold retention ribs creating localized areas of decreasedimpact resistance as well as the usual wall draft to permit removal ofthe product, or tub, from the forming mold. One primary disadvantagearising from this necessary wall draft concerns the mounting of theupper dishwasher rack supporting tracks in parallel.

In addition to the foregoing considerations which relate primarily tomounting and/or assembly procedures for large capacity front loadingmachines, the desirability of precluding tub discoloration and thedesirability for firewall separation of the tub and those electricalcomponents constituting a fire hazard are common to all automaticdishwashing machines. As regards plastic tub discoloration, it ispreferred to avoid the use of certain conventional strand typereinforcing fillers, such as chopped strand fiber glass, for the reasonthat their intersection with the interior plastic surface may provide ableed path for food stains to permeate the tub structure.

The prior art suggestions relating to the use of small capacity plastictubs of the top loading type, as in US. Pat. No. 2,691,986 and the useof separate plastic tub components, as in US. Pat. Nos. 2,877,778 and3,385,306 offer little in the way of guidelines as regards a practicalreduction to practice of a large capacity front loading tub for thereason that most of the problems requiring solution are not present insmaller and- /or top loading units and particularly those which employan enveloping metal housing.

The present invention is concerned with constructional and mountingdetails to compensate for thermal growth of the relatively large areatub walls as well as an integrally molded tub wall configurationproviding common wall means for the support of the tub and lowerdishwasher rack while other of the aforementioned matters are more fullydescribed and claimed in the following, commonly owned, copendingapplications:

Ser. No. 319,556, filed Dec. 29, 1972, for Double,

Reversed Mounting Boss for Plastic Tub;

Ser. No. 319,201,filed Dec. 29, 1972, for Fill Funnel Construction forPlastic Tubs;

Ser. No. 319,203, filed Dec. 29, 1972, for Front Loading DishwasherEmploying Plastic Tub Construction;

Ser. No. 319,348, filed Dec. 29, 1972, for Unit- I-Iandled RollerAssembly for Plastic Tubs;

Ser. No. 319,202, filed Dec. 29, 1972, for Radiused Mold Walls forPlastic Tubs;

Ser. No. 31,368, filed Dec. 22, 1972, for Angled Levelling Foot forDomestic Appliance;

Ser. No. 319,200, filed Dec. 29, 1972, for Torsionally Reinforced,Skeletal Support Frame for Plastic Tubs;

Ser. No. 319,557, filed Dec. 29, 1972, for Impact Protection for PlasticTub Employing Mold Retention Ribs,

Ser. No. 319,199, filed Dec. 29, 1972, for Plastic Tub Wall Alignmentfor Dishwasher Rack Mounting.

Elimination of the conventional front loading metal tub and thesubstitution therefor of a plastic tub necessitates the presence ofmounting and/or support structure to compensate for those inherentcharacteristics previously available in the use of a metal tub whichinclude a modulus of rigidity sufficient to preclude wall deformationand provide secure anchor points for component mountings and whose boxbeam" tub shape insures adequate resistance to external loading forces.It is apparent that if the advantages of the invention, as regardsdecreased cost and weight, are to be retained the necessary mounting andsupport structure must not, in effect, comprise a confining tub supporthousing. Rather, a purpose of the invention is to provide an operative,front loading dishwasher unit having a plastic tub whose outer wallscomprise the great majority of the outer dishwasher unit constructionand would actually be exposed to view prior to installation of thedishwasher unit within an outer decorative housing, which decorativehousing may comprise a free standing, portable unit or a permanentundercabinet installation.

SUMMARY OF THE INVENTION It is apparent that the relatively largesurface area tub walls having an exemplary wall thickness of less than0.2 inch will have a tendency to undergo substantial thermal growth as afunction of temperature variations to which the wash chamber issubjected during a normal wash cycle. The tendency, of course, is forthe walls to deform inwardly as a function of increasing temperaturegradient across the tub walls in response to increased wash chambertemperatures. The effect of such temperature gradient, i.e., thetemperature differential across the tub wall, is heightened by the factof the plastic composition which is a poor thermal conductor.

Substantial, inward tub wall deformation cannot be tolerated for reasonof obvious interference with moving dishwasher racks and the rotatingspray bar and the compensation for this thermal growth factorconstitutes one of two primary objects of the invention. The secondobjective relates to the use of a common integrally molded tub wallportion, on each tub sidewall, to support the tub on its base andprovide the lower dishwasher support tracks. Secondarily, theseintegrally molded portions interfit with, and are backed by, the metalbase assembly to preclude parts warpage and insure parallelism of thetracks.

It has been found that the requisite structural integrity can beimparted to the overall dishwasher and tub construction through the useof a metal base assembly and a relatively narrow (as compared to the tubdepth) metal collar upstanding from the base assembly and extendingacross the top and sidewalls of the tub immedi ately adjacent the openend thereof. The front, open end of the tub is then secured to thesurrounding, composite box beam collar and base assembly thus anchoringthe open end of the tub to a relatively rigid metal shape. The savingsin fabrication, cost and weight involved in bending a narrow metal strapinto an approximate U-shape to form a collar and then joining the sameto a base assembly as compared with the utilization of a complex metalshape to either form the tub or envelope a tub liner are obvious.

The tub itself is a unipartite, injection molded tub which ishomogeneous throughout and thus exhibits no surface exposed, reinforcingfibers along which food stains could permeate the tub structure. morespecifically, the tub is comprised of a homogeneous, unipartite,polypropylene based plastic.

Inward wall deformation may be precluded by forming the tub walls withan initial, unstressed outward bow so that thermal expansion of theplastic results only in a minimal increase in the outwardly bowed walls.This approach is entirely feasible insofar as the lower, top and backwalls of the tub are concerned; however, the formation of preformed bowsin the sidewalls is not readily accomplished by reason of the particularmolding procedures employed in the one piece tub molding hereindisclosed. This, broadly, for the reason that the multipart,contractible mold core used to form the tub is contracted vertically toclear the lower mold core part from the complex bottom configurationwhile the transverse dimensions of the tub forming mold core remainconstant throughout formation and removal of the tub. Thus the mold coresides used to form the tub sidewalls do not contract and product removaltakes place through surface to surface sliding contact between the tubsidewalls and mold core rendering impractical the integral formation ofoutwardly bowed sidewall portions. As to the remaining tub walls, i.e.,the lower, top and back walls, product removal does not involve slidingsurface to surface contact inconsistent with the formation of slightlybowed walls.

Although it is thought that for the purposes of the present invention;the foregoing brief description of the reasons why the tub sidewalls areplanar while the remainder of the tub walls include an integral,unstressed outward bow will suffice; reference may be had to theaforementioned copending application Ser. 319,202 for a more completedescription of the molding procedures.

The unstressed planar sidewalls are mechanically deformed, outwardly, toachieve substantially the same result as with the preformed wall how byapplying a deforming stress through the intermediary of separablefasteners anchored in the mounting collar.

The tub sidewalls are stepped inwardly adjacent the lower edges thereofto define horizontal ledges whose lower surfaces rest upon a metal baseassembly while the upper surfaces thereof provide the lower dishwasherrack supporting tracks.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front perspective of a frontloading dishwasher employing a plastic tub;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a section taken along line 3-3 of FIG. 1 as the part wouldappear prior to the mechanical intro duction of a wall deforming stress;and

FIG. 4 is a similar view illustrating the outward bow followingapplication of the applied stress.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 is illustrated afront loading dishwasher including a metal support frame 12 comprised ofa base assembly 14 and a tub mounting collar 16 on which is supported ahomogeneous, unipartite, plastic tub 18 as well as the remainder of theusual dishwasher components.

The opposite tub sidewalls 20, adjacent the lower edges thereof, arestepped inwardly to form ledges or horizontal walls 22 continuous withfurther downward extensions 24 of the tub sidewalls which merge with alower tub wall 26. The role of each wall 22 in performing, in effect, adual load support function on opposite surfaces thereof with theattendant saving in cost and assembly time as well as the avoidance ofan inventory requirement for separable components, will be obvious froman inspection of FIG. 2. Thus the lower and upper surfaces 28, 30 ofeach horizontal wall 22 provide opposed load bearing surfacesrespectively engaged by upstanding side panels 32 and wheels 34 on whichthe lower dishwasher rack 36 is mounted. The base assembly side panels32 are interconnected by a bottom plate 38 underlying the lower tub walland positioning the side panels in closely spaced relation to tubsidewall extensions 24.

Each of the upper, lower and rear tub walls are preformed with anunstressed outward bow as best illustrated by the outwardly bowed upperwall 40 in FIG. 1. A similar outward bow is mechanically induced in thesidewalls 20, which are preformed as unstressed planar walls, after thefashion illustrated in FIGS. 3 and 4.

It will be recalled from the foregoing discussion that it is notfeasible to preform the sidewalls in the desired, bowed configuration;however, such sidewalls are preformed with integral mounting bosses 42outstanding from the exterior sidewall surfaces to accept a threadedfastener 44 anchored in an offset portion 46 of the mounting collar 16.The spacing of offset portion 46 of mounting collar 16 relative to theinitial unstressed position of tub wall 20 and mounting boss 42 (FIG. 3)is calculated in light of known thermal growth characteristics toinduce, upon engagement of fastener 44 as in FIG. 4, an outwarddeformation or bow of sidewall 20, from the unstressed phantom lineposition, which is sufficient to preclude that inward movement of thesame which would result from the expected thermal gradient across theunstressed planar sidewall 20.

While the background discussion of this specification is relatedprimarily to front-loading dishwashers of the type nonnally adapted fora permanent undercounter installation as opposed to the type ofdishwasher having a hinged top closure for top-loading, it should beemphasized that many such machines are commercially produced andpurchased for indefinite use as a freestanding model adaptable at alater time by the owner to a built-in unit beneath a kitchen countertopto blend with the matching cabinet structure of the kitchen. Generally,the difference between the unit designed as a convertible and the unitto be immediately permanently installed is the inclusion of side, rearand top cabinet appearance panels to the basic unit structure asdesigned for permanent installation. Therefore. it should be understoodthat the present invention is specifically directed to the front-loadingtype of dishwasher structure whether of the generally lower-cost unithaving no appearance cabinet enclosure or the more elaborate.temporarily portable unit designed for later modification for use in afixed location.

I claim:

I. In a front loading dishwasher including a plastic tub having agenerally rectangular cross-section, a tub support frame including abase assembly underlying the lower tub wall and a tub mounting collarupstanding from said tub support frame engaging the top and sidewalls ofsaid tub adjacent the open front end thereof in backing relationthereto, the improvement comprising; horizontal wall means integral witha lower portion of each said sidewall defining opposed load bearingsurfaces on opposite sides of each said horizontal wall means forrespective support of a lower dishwasher rack on the upper of said loadbearing surfaces and support of the tub on said base assembly on thelower of said load bearing surfaces; and said base assembly includingspaced support panels having upper tub supporting edges in supportingengagement with said lower load bearing surfaces.

2. The dishwasher of claim 1 wherein the lower portion of each of saidsidewalls extend inwardly to define said horizontal wall means anddownwardly therefrom to merge with a lower bottom tub wall; and theupper and lower load bearing surfaces on said horizontal wall meansbeing continuous with the inner and outer surfaces of said sidewalls,respectively.

3. In a front loading dishwasher including a unipartite plastic tub ofhomogeneous construction defining a wash chamber of generallyrectangular cross-section, a tub support frame including a base assemblyunderlying the lower tub wall and a tub mounting collar upstanding fromthe front end of said tub support frame engaging the top and sidewallsof said tub adjacent the open front end thereof and remote from theclosed tub back wall, the improvement comprising; at least the sidewallsof said tub being bowed outwardly, through stressed securing meansanchored in said mounting collar a preselected distance which issufficient to compensate for inward movement thereof resulting fromthermal expansion during the operation of the dishwasher, wherebyinterference of said sidewalls with movable dishwasher racks and arotating spray bar is avoided.

4. The dishwasher of claim 3 wherein said sidewalls include integralmounting bosses outstanding therefrom; and said securing means extendingthrough said mounting collar and into said bosses to terminate short ofthe wash chamber.

5. the dishwasher of claim 4 wherein said lower, top and back wallsinclude an unstressed outward bow.

6. In a front loading dishwasher including a unipartite plastic tub ofhomogeneous construction defining a 7 wash chamber of generallyrectangular cross-section, a tub support frame including a base assemblyunderlying the lower tub wall and a tub mounting collar upstanding fromthe front end of said tub support frame engaging the top and sidewallsof said tub adjacent the open front end thereof in backing relationthereto, the improvement comprising: horizontal wall means integral witha lower portion of each of said sidewalls defining opposed load bearingsurfaces on opposite sides of each said horizontal wall means forrespective support of a lower dishwasher rack on the upper of said loadbearing surfaces and support of the tub on said base assembly on thelower of said load bearing surfaces and said base assembly includingspaced support panels having upper tub supporting edges in supportingengagement with said lower load bearing surfaces, and at least saidsidewalls of said tub being mechanically bowed outwardly a preselecteddistance which is sufficient to compensate for inward movement thereofresulting from thermal gradients across the unstressed, planar sidewallsduring the operation of the dishwasher.

1. In a front loading dishwasher including a plastic tub having agenerally rectangular cross-section, a tub support frame including abase assembly underlying the lower tub wall and a tub mounting collarupstanding from said tub support frame engaging the top and sidewalls ofsaid tub adjacent the open front end thereof in backing relationthereto, the improvement comprising; horizontal wall means integral witha lower portion of each said sidewall defining opposed load bearingsurfaces on opposite sides of each said horizontal wall means forrespective support of a lower dishwasher rack on the upper of said loadbearing surfaces and support of the tub on said base assembly on thelower of said load bearing surfaces; and said base assembly includingspaced support panels having upper tub supporting edges in supportingengagement with said lower load bearing sUrfaces.
 2. The dishwasher ofclaim 1 wherein the lower portion of each of said sidewalls extendinwardly to define said horizontal wall means and downwardly therefromto merge with a lower bottom tub wall; and the upper and lower loadbearing surfaces on said horizontal wall means being continuous with theinner and outer surfaces of said sidewalls, respectively.
 3. In a frontloading dishwasher including a unipartite plastic tub of homogeneousconstruction defining a wash chamber of generally rectangularcross-section, a tub support frame including a base assembly underlyingthe lower tub wall and a tub mounting collar upstanding from the frontend of said tub support frame engaging the top and sidewalls of said tubadjacent the open front end thereof and remote from the closed tub backwall, the improvement comprising; at least the sidewalls of said tubbeing bowed outwardly, through stressed securing means anchored in saidmounting collar a preselected distance which is sufficient to compensatefor inward movement thereof resulting from thermal expansion during theoperation of the dishwasher, whereby interference of said sidewalls withmovable dishwasher racks and a rotating spray bar is avoided.
 4. Thedishwasher of claim 3 wherein said sidewalls include integral mountingbosses outstanding therefrom; and said securing means extending throughsaid mounting collar and into said bosses to terminate short of the washchamber.
 5. the dishwasher of claim 4 wherein said lower, top and backwalls include an unstressed outward bow.
 6. In a front loadingdishwasher including a unipartite plastic tub of homogeneousconstruction defining a wash chamber of generally rectangularcross-section, a tub support frame including a base assembly underlyingthe lower tub wall and a tub mounting collar upstanding from the frontend of said tub support frame engaging the top and sidewalls of said tubadjacent the open front end thereof in backing relation thereto, theimprovement comprising: horizontal wall means integral with a lowerportion of each of said sidewalls defining opposed load bearing surfaceson opposite sides of each said horizontal wall means for respectivesupport of a lower dishwasher rack on the upper of said load bearingsurfaces and support of the tub on said base assembly on the lower ofsaid load bearing surfaces and said base assembly including spacedsupport panels having upper tub supporting edges in supportingengagement with said lower load bearing surfaces, and at least saidsidewalls of said tub being mechanically bowed outwardly a preselecteddistance which is sufficient to compensate for inward movement thereofresulting from thermal gradients across the unstressed, planar sidewallsduring the operation of the dishwasher.